The objectives of this proposal are to precisely define how various factors influence the patterns of particle deposition which occur during breathing and to use aerosols as a probe of lung function. Specifically, we propose: 1) to explore how breathing pattern and lung volume influence deposition site for different sized aerosols; 2) to use tracer aerosols to describe the distribution of non-ventilated areas in the lung and to investigate variations in parenchymal deposition; 3) to compare measurements of aerosol deposition in different species with predictions based on scaling theory; 4) to characterize aerosol deposition in the expiration direction; 5) to utilize magnetic aerosols to quantify long-term particle clearance and particle rotation in the lung. Most of these aims will be carried out by analyzing small samples of dried or frozen lungs and by using the gamma camera, autoradiography, and piece analysis to measure the amount of aerosol retained in different lung regions. Also available to us is a servo-pressure control system which can be used to simulate any breathing pattern at any specified lung volume. Another major resource is personnel and instrumentation for the measurement of very small magnetic fields. This work is of significance for two reasons. First, since inhalation is the primary entry route for agents that cause environmental, occupational, and infectious disease, it is important to understand better how and where particles deposit within the respiratory tract. Thus, this information will be of value in understanding and controlling environmental hazards. Secondly, it will be of use in devising more rational strategies for pharmacologic and therapeutic aerosols. Finally, some aspects of this proposal will utilize aerosols in order to gain a better understanding of pulmonary physiology.